The invention relates to a capacitor, particularly a multi-layer capacitor with inner electrodes of a base metal and with a ceramic dielectric which essentially comprises a dielectric composition of a barium-calcium-manganese-zirconium-titanate as a basic material.
Multi-layer capacitors are used, inter alia, for decoupling and buffering the power supply of processors, particularly high-power microprocessors. During operation in the high-power mode, these active electronic components generate much heat, and even with an intensive cooling the temperature of a high-power processor in permanent operation is between 70xc2x0 C. and 80xc2x0 C. Conventional multi-layer capacitors of the specification Y5V have only 20% of their rating (xcex94C≈80%) at an operating temperature of 80xc2x0 C. For manufacturing microprocessors, capacitors of the specification X7R are therefore preferably used, because they still have 85% of their rating (xcex94C less than xc2x115%) at a temperature of 125xc2x0 C. The specific capacitance of an X7R capacitor is, however, approximately 5 times lower at room temperature than that of a capacitor of the specification Y5V, so that an X7R capacitor must have larger dimensions, for example, the dimensions of a 1 xcexcF X7R capacitor must be at least of the size 1206 (length 0.12 nominal, width 0.06 nominal). For capacitances of  greater than 5 xcexcF, the more expensive tantalum capacitors can therefore only be used until now.
A ceramic multi-layer capacitor having a plurality of ceramic layers on the basis of doped BaTiO3 and a plurality of electrode layers mainly comprising nickel is already known from WO 98/54737, in which capacitor the ceramic layers and the electrode layers are alternately stacked so that they constitute a multi-layer structure and are implemented on both side faces with electric connections contacting the electrode layers, and in which the main components of the doped BaTiO3 are defined by the general formula
(Ba1xe2x88x92axe2x88x92bCaaDyb)(Ti1xe2x88x92cxe2x88x92dxe2x88x92exe2x88x92fZrcMndNbe)fO3+∂. This capacitor is suitable for DC applications at high temperatures.
It is an object of the present invention to provide a capacitor having a ceramic dielectric and at least two electrodes, in which the dielectric essentially comprises a dielectric ceramic composition of a barium-calcium-manganese-zirconium-titanate as a basic material, which capacitor is suitable for DC applications at high temperatures and has smaller dimensions than the prior-art capacitor.
According to the invention, the object is solved by a capacitor having a ceramic dielectric and at least two electrodes, in which the dielectric essentially comprises a dielectric ceramic composition of a barium-calcium-manganese-zirconium-titanate as a basic material having the composition (Ba1xe2x88x92xCax)y[Ti1xe2x88x92axe2x88x92bxe2x88x92cxe2x88x92dZraMnbNbcDyd]O3 with 0 less than axe2x89xa60.25, 0 less than bxe2x89xa60.015, 0.001xe2x89xa6cxe2x89xa60.01, 0.005xe2x89xa6dxe2x89xa60.02, 0 less than xxe2x89xa60.20, 1.001xe2x89xa6yxe2x89xa61.014, 0.0005xe2x89xa6zxe2x89xa60.03.
Within the scope of the present invention, it is preferred that the general formula is (Ba1xe2x88x92xCax)y[Ti1xe2x88x92axe2x88x92bxe2x88x92cxe2x88x92dZraMnbNbcDyd]O3 with 0 less than axe2x89xa60.25, cxe2x88x920.5dxe2x89xa6bxe2x89xa60.015, 0.001xe2x89xa6cxe2x89xa60.01, 0.005xe2x89xa6dxe2x89xa60.02, 0 less than xxe2x89xa60.20, 1.001xe2x89xa6yxe2x89xa61.014, 0.0005xe2x89xa6zxe2x89xa60.03.
It is also preferred that the dielectric ceramic composition comprises, as a further additive, SiO2 in a quantity z with 0.0005xe2x89xa6zxe2x89xa60.03 mol/unit.
Furthermore, it is preferred that the electrodes consist of nickel or a nickel-containing alloy.
The invention also relates to a dielectric ceramic composition of a barium-calcium-manganese-zirconium-titanate as a basic material having the general formula (Ba1xe2x88x92xCax)y[Ti1xe2x88x92axe2x88x92bxe2x88x92cxe2x88x92dZraMnbNbcDyd]O3 with 0 less than axe2x89xa60.25, 0 less than bxe2x89xa60.015, 0.001xe2x89xa6cxe2x89xa60.01, 0.005xe2x89xa6dxe2x89xa60.02, 0 less than xxe2x89xa60.20, 1.001xe2x89xa6yxe2x89xa61.014,0.0005xe2x89xa6zxe2x89xa60.03.
It is preferred that the general formula is (Ba1xe2x88x92xCax)y[Ti1xe2x88x92axe2x88x92bxe2x88x92cxe2x88x92dZraMnbNbcDyd]O3 with 0 less than axe2x89xa60.25, cxe2x88x920.5dxe2x89xa6bxe2x89xa60.015, 0.001xe2x89xa6cxe2x89xa60.01,0.005xe2x89xa6dxe2x89xa60.02,0 less than xxe2x89xa60.20, 1.001xe2x89xa6yxe2x89xa61.014, 0.0005xe2x89xa6zxe2x89xa60.03.
It is also preferred that the composition comprises, as a further additive, SiO2 in a quantity z with 0.0005xe2x89xa6zxe2x89xa60.03 mol/unit.
Such a dielectric ceramic composition is characterized by a low sintering temperature of 1200xc2x0 C. Due to its fine grain structure it is suitable for very thin dielectric layers. Capacitors with a dielectric comprising this material have an extraordinarily high breakdown voltage  less than 100 V/xcexcm and are resistant to aging when they are DC operated. With this dielectric ceramic composition, capacitors having a high capacitance and small dimensions can be manufactured, while they simultaneously have a long lifetime.
Within the scope of the present invention it is preferable that the electrodes comprise nickel or a nickel-containing alloy.
These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.